Behavioral and neurochemical differences in an inbred strain of rats.

The spontaneous motility of 75 Sprague-Dawley rats obtained from an inbred strain was found to vary widely. To test the hypothesis that heterogeneity in motility is accompanied by heterogeneity in neurochemical and vegetative function variables, the median motility score was used to divide the animals into high and low motility groups. Subgroups of high and low motile animals were compared on fecal pellet scores and on dopamine, dihydroxyphenyl acetic acid and homovanillic acid content of the corpus striatum. Significant differences were obtained between the two groups, indicating that even in an inbred strain considerable heterogeneity (possibly representing further subtypes) may exist. The theoretical and experimental implications of these findings are discussed.